Techniques for generating composite structures that combine metal and polymer compositions

This application claims priority benefit of the United States Provisional patent application titled, “TECHNIQUES FOR COMPOSITE STRUCTURES THAT COMBINE METAL AND POLYMER COMPOSITIONS” filed on Jan. 6, 2022 and having Ser. No. 63/297,022. The subject matter of this related application is hereby incorporated herein by reference.

The various embodiments relate generally to additive manufacturing and, more specifically, to techniques for generating composite structures that combine metal and polymer compositions.

Additive manufacturing, also known as three-dimensional (3D) printing, is the construction of a three-dimensional object by sequentially depositing one material layer at a time via a special printing machine to build out the three-dimensional object or by adding material to build out the three-dimensional object via some other technique. In many additive manufacturing processes, the material layers can be deposited, joined, or solidified under computer control that is based on a computer-aided design (CAD) or other a digital 3D model to form a multi-material structure. Because multi-material structures can have superior physical properties, they are tremendously important in applications where strong, lightweight mechanical systems are needed, such as automotive, aerospace, and construction applications. Further, multi-material structures frequently fulfill multiple functions, such as when a given structure serves as a structural component that also is corrosion- and environmental agent-resistant.

One drawback to additive manufacturing is that there is generally poor mechanical coupling between the different materials that are included in a multi-material component. For example, 3D-printed polymers that are formed on the surfaces of dissimilar substrates (such as a metals or ceramics) are known to have poor adhesion to those surfaces. Consequently, the different materials making up a multi-material component behave as separate structural elements as opposed to contributing collectively to the mechanical properties of the overall component. As a result, the multi-material component cannot act as a monolithic structure in response to stresses, impacts, and the like. For example, a polymeric skin that is 3D printed onto a surface of a metallic structural member may closely conform to the surface of the structural member, but may not contribute to the rigidity of the metallic structural member due to poor or nonexistent mechanical coupling between the polymeric skin and the surface of the metallic structural member. In such a situation, the polymeric skins may add little or no structural strength or rigidity to the metallic structural member.

Another drawback to additive manufacturing is that the polymeric materials typically employed in 3D-printing can be highly sensitive to the way in which those materials are deposited. For example, 3D-printer nozzle velocity, deposition temperature, deposition rate, and direction of deposition can all significantly affect the physical properties of a 3D-printed polymer. As a result, the physical properties of 3D-printed polymers can be undesirably variable and difficult to predict, which can be problematic when such polymers are included in components that are load-bearing and/or receive impacts. These issues can be particularly prevalent for fiber-reinforced polymers, which can be highly anisotropic.

As the foregoing illustrates, what is needed in the art are more effective additive manufacturing techniques that involve polymers and metallic substrates.

A multi-material structure includes: a structural member that includes an isotropic material and at least one open-cell void formed in the isotropic material; and a skin that includes a polymetric material and is disposed on a surface of the structural member and within the at least one open-cell void.

A multi-material structure includes: a structural member that includes an isotropic material; and a skin that includes a polymetric material, is disposed on a surface of the structural member, and has at least one closed-cell void that is disposed on the surface of the structural member and contains an adhesive material.

A method for fabricating a multi-material structure, the method comprising: forming a structural member with at least one open-cell void that is formed on a surface of the structural member; depositing a first portion of a polymeric skin on the surface; and depositing a second portion of the polymeric skin within the at least one open-cell void.

A method for fabricating a multi-material structure, the method comprising: forming a structural member with a surface; forming a polymeric skin on the surface by depositing a first portion of a polymeric material on a first portion of the surface; forming at least one open-cell void on the surface by depositing a second portion of a polymeric material proximate a second portion of the surface; and injecting an adhesive into the at least one closed-cell void

At least one technical advantage of the disclosed techniques relative to the prior art is that the disclosed techniques enable the fabrication of a multi-material structure that has improved mechanical coupling between different materials included in the multi-material structure relative to what can be achieved using conventional techniques. Consequently, the multi-material structures generated using the disclosed techniques behave mechanically as single monolithic members instead of collections of separate discrete elements. Another technical advantage of the disclosed techniques is that 3D-printed polymers can be deposited or formed with predictable physical properties. Consequently, when generating a multi-material structure using the disclosed techniques, anisotropic, 3D-printed polymers can be formed and oriented to enhance the strength and/or rigidity of the multi-material structure relative to what can be achieved using conventional techniques. These technical advantages provide one or more technological advancements over prior art approaches.

For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one embodiment may be incorporated in other embodiments without further recitation.

In the following description, numerous specific details are set forth to provide a more thorough understanding of the various embodiments. However, it will be apparent to one of skill in the art that the inventive concepts may be practiced without one or more of these specific details.

schematically illustrates a cross-sectional view of a multi-material structure, according to various embodiments. Multi-material structurecan be any structure or component of a structure that is fabricated via an additive manufacturing process and include multiple materials. In the embodiment depicted in, multi-material structureis a structural member that includes an endoskeletonand a polymeric skinthat is formed on a surfaceof endoskeleton. According to various embodiments, polymeric skinis mechanically and/or chemically (e.g., via adhesive) coupled to endoskeleton, so that multi-material structurebehaves as a single monolithic structure, rather than as an assembly of separate parts that are discretely joined together by fasteners, welds, and/or the like. Thus, phenomenon acting on multi-material structure, such as physical, thermal, and/or chemical stresses, affect the multi-material components of multi-material structuresimultaneously. For example, in the embodiment illustrated in, polymeric skinand endoskeletoneach contribute simultaneously to the shock absorption of multi-material structurewhen a physical impact is received thereby. In other examples, polymeric skinand endoskeletoneach contribute simultaneously to how multi-material structureresponds to heat transfer, a bending or torsion load, and the like. By contrast, in an assembly of separate parts that are discretely joined together, the effects of a phenomenon acting on the assembly (e.g., force, thermal energy, vibration, and the like) passes through points of concentration from one element of the assembly to the other, such as bolts, welds, and the like. Thus, such an assembly generally behaves as a collection of discrete parts and not as a monolithic component.

According to various embodiments, multi-material structurebehaves as a single monolithic structure in response to a certain phenomenon, such as physical, thermal, and/or chemical stresses. In the embodiment illustrated in, polymeric skinis mechanically coupled to endoskeletonvia one or more open-cell voids. Open-cell voidsare formed on one or more surfaces of endoskeletonand contain a portion of polymeric skinas shown. In some embodiments, polymeric skinis further chemically coupled to endoskeletonvia an adhesive (not shown) that is disposed in one or more closed-cell voids.

Endoskeletonis a structural member or other rigid element of multi-material structure, and includes a central cavity, and one or more open-cell voids. In some embodiments, endoskeletoncan be composed of a metallic, polymeric, wood, ceramic, or composite material. In some embodiments, endoskeletonis comprised of an isotropic material, such as a metal or ceramic. In some embodiments, endoskeletonis formed via any technically feasible manufacturing technique or techniques, such as extrusion, pultrusion, rolling, bending, welding, forging, stamping, and/or the like. In the embodiment illustrated in, endoskeletonis configured as an extruded metallic profile, and open-cell voidscan be formed via the extrusion process. In other embodiments, open-cell voidscan be formed via separate processes, such as machining, welding, and the like. Thus, in such embodiments, open-cell voidsare added to endoskeleton.

Open-cell voidscan be concave features that are formed on one or more surfaces of endoskeletonand configured so that a portion of polymeric skincan be deposited therein when polymeric skinis formed on endoskeleton. Thus, each open-cell voidincludes at least one openingthrough which a portion of polymeric skincan be deposited. In the embodiment illustrated in, open-cell voidsare formed on four surfaces of endoskeleton. In other embodiments, open-cell voidsare not formed on all surfaces of endoskeleton, and instead are formed on one, two, or three surfaces of endoskeleton.

In some embodiments, one or more of open-cell voidsincludes a roughened surface, such as surfacewithin the open-cell voidformed on an upper surface of endoskeleton. In such embodiments, the increased surface roughness of surfaceenhances the mechanical coupling of the portion of polymeric skinthat is disposed within the associated open-cell void.

In some embodiments, endoskeletonincludes one or more cavities, such as central cavity. In some embodiments, such cavities may remain hollow upon completion of the fabrication of multi-material structure. In other embodiments, such cavities may be filled with a different material than that of endoskeleton. For example, in some embodiments, central cavitycan be filled completely or partially with a volumetric material or structure, such as a regular structure (e.g. a 3D-printed honeycomb) and/or a stochastic structure (e.g., a foam). In such embodiments, the stochastic structure can be added via one or more holes (not shown in) drilled or otherwise formed in endoskeletonor through endoskeletonand polymeric skin.

Polymeric skincan be any 3D printed polymer that is deposited, printed, and/or formed on one or more surfaces of endoskeleton. The polymeric material that forms polymeric skincan include any technically feasible polymer that can be deposited via a 3D-printing process, such as fused deposition modeling (FDM). FDM, also known as fused filament fabrication (FFF), deposits a thermoplastic layer by extruding thermoplastic filaments or pellets, such as acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA), through a heated nozzle. The melted material is applied to a substrate layer by layer to a build a structure, such as polymeric skin. Each layer is laid down one at a time until the part is complete.

Examples of suitable polymeric materials for use in polymeric skininclude ABS, PLA, polyetherimide (PEI) (also referred to as ULTEM®), polyether ether ketone (PEEK), and/or other thermoplastics. In some embodiments, the polymeric material includes a fiber-reinforced polymer. In such embodiments, certain fibers are included in the polymeric material, such as carbon fiber, glass fiber, natural fibers, and/or the like. In such embodiments, the reinforcing fiber can be a microfiber that is mixed into the polymer before or during the deposition process or a continuous fiber that is, for example, fed from a spool during the deposition process.

In some embodiments polymeric skinis formed with closed-cell voidsthat contain or are filled with an adhesive (not shown infor clarity). In such embodiments, the adhesive further mechanically couples polymeric skinto endoskeleton, so that polymeric skindoes not behave like a separate structural member from endoskeleton. Instead, the additional mechanical coupling provided by adhesive disposed in closed-cell voidsenables polymeric skinto respond in conjunction with endoskeleton, for example in response to an impact, a bending load, a torsional load, thermal stresses, and the like. In such embodiments, the adhesive can be injected into closed-cell voidsvia one or more injection holes (not shown in) drilled or otherwise formed in polymeric skin, for example in a process subsequent to the formation of polymeric skin. Thus, in such embodiments, closed cell voidsmay initially be formed during the deposition of polymeric skinand have no openings. One embodiment of a closed cell voidand associated injection holes is described below in conjunction with.

is a more detailed illustration of multi-material structureof, according to various embodiments. As shown, closed cell voidsare disposed between an external surfaceof endoskeletonand an internal surfaceof polymeric skin. As noted above, in some embodiments, polymeric skinis deposited via a 3D-printing process so that closed-cell voidis formed at specified locations between external surfaceand internal surface. In some embodiments, the locations of closed-cell voidsare selected to correspond to areas of external surfacewhere relatively large relative motion between endoskeletonand polymeric skinis predicted under certain conditions and/or loads. Alternatively or additionally, in some embodiments, the locations of closed cell voidsare selected to correspond to areas of external surfacewhere high strain of endoskeletonand polymeric skinis predicted under certain conditions and/or loads.

In some embodiments, multi-material structureincludes one or more injection holesfor the injection of an adhesiveinto closed-cell voids. In some embodiments, each closed-cell voidis coupled to two or more injection holes, so that a suitable adhesivecan be injected via one injection hole and air can escape via a different injection hole.

In some embodiments, to avoid collapse of closed-cell voidsduring deposition of polymeric skin, a widthof each closed-cell voidis limited. In such embodiments, the collapse of closed-cell voidsis avoided by providing support regions(dashed line) of polymeric skinthat are disposed between closed-cell voidsand in contact with external surface. The sizeof support regionscan be selected by one of skill in the art based on various factors, including rigidity of polymeric skinas deposited on external surface, widthof closed-cell voids, a depthof closed-cell voids, an expected physical load, an expected thermal load, and/or the like.

In the embodiments described above in conjunction with, multi-material structureincludes both open-cell voidsand closed-cell voids. In some embodiments, multi-material structureincludes open-cell voidsin endoskeletonbut no closed-cell voidsin polymeric skin. Alternatively, in some embodiments, multi-material structureincludes closed-cell voidsin polymeric skinbut no open-cell voidsin endoskeleton.

According to various embodiments, polymeric skinis deposited on and mechanically coupled to endoskeletonvia an additive manufacturing process in which specific geometric locations within multi-material structureare associated with specific values of one or more process parameters. In some embodiments, each specific geometric location is associated with specific values of process parameters for formation of polymeric skinvia a data structure, such as an extended non-uniform rational B-spline (NURBS). In the embodiments, the data structure can include a NURBS that describes the geometrical configuration of the various materials included in multi-material structure, such as the various different layers of 3D-printed materials multi-material structure. In addition the data structure includes an extended NURBS that associates each of a plurality of geometric locations with specific values for one or more process parameters (for example, formation of polymeric skin). Thus, the extended NURBS does not merely describe the geometry of multi-material structure. In addition, the extended NURBS enables specific manufacturing processes to be performed in the formation of multi-material structure, where each manufacturing process includes specified values for various process parameters at a plurality of geometrical locations within multi-material structure. Examples of such process parameters include deposition temperature, material flowrate, deposition nozzle velocity and acceleration, and the like. Embodiments of such an additive manufacturing process are described below in conjunction with.

sets forth a flowchart of method steps for fabricating a multi-material structure, according to various embodiments.depict the fabrication of multi-material structure, according to various embodiments. Although the method steps are described in conjunction with the multi-material structure of, persons skilled in the art will understand that fabrication of any multi-material structure with the method steps, in any order, is within the scope of the embodiments. Further, persons skilled in the art will understand that any suitable computer-aided manufacturing system configured to perform the method steps, in any order, is within the scope of the embodiments. An embodiment of one such system is described below in conjunction with.

Prior to the method steps, a geometry of multi-material structureis determined. Thus, the relative locations of each material component of multi-material structureis specified, for example via a conventional NURBS. The geometry that is determined may be based on various functional requirements and design constraints, and may be generated manually via a computer-aided design package, a generative design process, or any other technically feasible design generation process. In some embodiments, the conventional NURBS includes a network of geometry control points that define the shape of one or more component surfaces and/or geometries in 3D space. An embodiment of one such NURBS is described below in conjunction with.

is a tabular representationof a NURBS that defines the geometry of a multi-material structure, according to various embodiments.is a graphical representationof the NURBS and the associated geometry defined thereby, according to various embodiments. As shown in, tabular representationof the NURBS includes information associated with a plurality of geometric control pointsthat are each positioned in 3D space (as shown in). Thus, for each geometric control point, there is an x-location value, a y-location value, and a z-location valuein tabular representation, which together indicate the geometric position in 3D space for that geometric control point. In some embodiments, tabular representationof the NURBS includes information regarding the order of the polynomial used to describe the NURBS. In addition, for each geometric control point, tabular representationincludes a valuefor a knot vector (which generally ranges from 0 to 1) and a weight. The valuefor the knot vector and the valuefor the weight affect the position of a surface(shown in) in 3D space that is defined by the NURBS, where surfacecan be a surface of a particular component of a multi-material structure, such as endoskeleton, polymeric skin, and the like. In particular, the valuefor the knot vector and the valuefor the weight cause surfaceto be attracted to or repelled from the associated control point. In some instances, surfaceis referred to as a u,v domain (represented by a grid) of the NURBS that is defined in a 2D parametric space.

Returning to, prior to the method steps, values for various process parameters for the fabrication of multi-material structureare determined. According to various embodiments, via an extended NURBS, values for the various process parameters are associated with specific geometric locations that are included in the defined geometry for multi-material structure. Thus, at each specific geometric location associated with a particular component of multi-material structure, the process for generating that particular component of multi-material structureis defined. For example, for polymeric skin, at each specific geometric location, values are defined for process parameters such as nozzle velocity, nozzle orientation, deposition temperature, nozzle acceleration, material flow rate, air gap between the nozzle and the substrate or receiving surface, and the like. The process parameters can then be converted to computer-numerical-control (CNC) commands for the fabrication of the structure, such as G-code or any other suitable CNC programming language.

It is noted that the data structure that includes the conventional NURBS and the extended NURBS defines both the geometry of polymeric skinand a specific process for manufacturing polymeric skin. For example, the specific process can be optimized or otherwise configured for the geometry of polymeric skin. Such a process can include nozzle velocities, nozzle trajectories, deposition temperatures, and the like that avoid process-related flaws in polymeric skin, such as delamination, poorly formed radii, collapsed structures (due to lack of supporting material), and the like. Furthermore, in some embodiments, such a process can include nozzle velocities and/or nozzle trajectories that result in a targeted orientation of reinforcing fibers included in polymeric skin. This is because reinforcing fibers are known to substantially align with the direction of travel of a 3D printing nozzle. Thus, the process defined by embodiments of the extended NURBS described herein enables the incorporation of the anisotropic properties of 3D-printed polymers into multi-material structure. By contrast, conventional computer-aided-manufacturing systems receive the geometrical information for a multi-material structure that is to be fabricated, for example from a digital model of the structure that can be similar to the conventional NURBS described above. Conventional computer-aided-manufacturing systems then perform an automated generation of CNC commands for the fabrication of the structure. For example, G-code operations for controlling a 3D-printing process can be automatically generated based on the geometrical information for the structure, and typically involve slicing the structure into a plurality of layers to be formed sequentially in an automated 3D-printing process. Such a process is inherently unable to tailor process parameters for the 3D-printing process to a specific geometry, and instead selects values for process parameters, such as nozzle velocities and trajectories, that are optimal for the formation of the sequence of layers used to generate the structure. Thus, conventional approaches are unable to perform 3D-printing processes in which process parameters are tailored to the geometry of a specific structure; instead, the process parameters are adjusted based on the geometry of a specific slice of the structure.

is a tabular representationof an extended NURBS that defines a fabrication process for a multi-material structure, according to various embodiments.is a graphical representationof the extended NURBS and a geometryof the multi-material structure, according to various embodiments. As shown in, tabular representationof the NURBS includes information associated with a plurality of process parameter control pointsthat are each positioned in 3D space (as shown in). More specifically, each of the plurality of process parameter control pointsis positioned on geometry, which is disposed in 3D space. Thus, for each process parameter control point, there is an x-location value, a y-location value, and a z-location valuein tabular representation, which together indicate the geometric position in 3D space for that process parameter control point. It is noted that each process parameter control pointis constrained to be disposed on or within geometry, thereby enabling specific process parameter values to be associated with each location on or within geometry.

In some embodiments, tabular representationof the extended NURBS includes information regarding the order of the polynomial used to describe the extended NURBS. In addition, for each process parameter control point, tabular representationincludes a valuefor a knot vector, a weight, and a valuefor each of N process parameters. The valuefor the knot vector and the valuefor the weight cause a surface (not shown) in a parametric space to be attracted to or repelled from the associated process parameter control point. Unlike geometry, which defines a geometry in 3D space, the surface in parametric space cannot be graphically visualized relative to geometry. However, the shape of the surface in parametric space can define values for process parameters. Thus, for specific locations disposed on or within geometry, there is an associated value for each of N process parameters. Examples of the N process parameters include deposition nozzle velocity and acceleration, deposition temperature, material flow rate, air gap between the deposition nozzle and the receiving surface, and the like. In some embodiments, the values for such defined process parameters can influence the shape of the extended NURBS and indicate to a designer that a specified geometrical shape of a structure may not be readily manufactured due to specific features, such as radii that are too small or a ramp that is too severe for a particular material being deposited. For example, based on such an indication provided by process parameters included in the extended NURBS, the designer may modify the specified geometrical shape to be more readily manufacturable. Thus, in such embodiments, values for the defined process parameters may be selected based on a specific material included in polymeric skinand on the specified geometry of polymeric skinto be formed.

Returning to, a computer-implemented methodbegins at step, where a baseis formed for a fabrication assembly, as shown in. Fabrication assemblyenables fabrication of multi-material structure, for example by supporting portions of polymeric skinthat would otherwise collapse. In the embodiment illustrated in, an end effector(such as a 3D printing nozzle) of a computer-aided-manufacturing system (not shown) deposits a plurality of layers of material to form base.

Generally, the deposition nozzle trajectory, material flowrate, and/or other process parameters are implemented via CNC commands or CNC machine code, such as G-code. In some embodiments, baseis formed via a conventional 3D-printing process, for example via FDM. Therefore, in such embodiments, the motions and other actions of end effectorare controlled by CNC commands that are generated by a conventional machine code generator. As noted previously, a conventional machine code generator automatically converts the 3D geometry of an object to be 3D printed (e.g., base) into a usually vertical stack of contour slices and generates machine code suitable for following the trajectories associated with the formation of such contour slices. Alternatively, in some embodiments, baseis formed via a 3D-printing process that employs values for process parameters included in an extended NURBS for multi-material structure. In such embodiments, the CNC commands that cause end effectorto form baseare generated from end effector trajectories, material flowrate values, and other process parameters that are included in the extended NURBS. Thus, such CNC commands are not generated by a conventional machine code generator.

Because baseis ultimately sacrificed in the fabrication of multi-material structure, the specific material used for basegenerally may have few structural or strength constraints. Instead, the specific material used for basemay be selected based on factors that facilitate fabrication of multi-material structure. For example, in some embodiments, a material for baseis selected based on adhesion to the material used for polymeric skinand/or a surface roughness that may affect the surface roughness of polymeric skin.

In step, polymeric skinfor one or more blind surfaces of endoskeletonare deposited, as shown in. In some embodiments, a blind surface of endoskeletonis a surface of endoskeletonthat may not accessible while a portion of polymeric skinis being deposited on another surface of endoskeleton. In some embodiments, a blind surface can be a surface of endoskeletonthat does not include an open-cell void. In some embodiments, polymeric skinis formed to include one or more closed-cell voidson exposed surfaces. Thus, in such embodiments, closed-cell voidsare not yet completely closed, because endoskeletonis not yet positioned adjacent to exposed surfaces.

In step, endoskeletonis inserted into baseof fabrication assembly, as shown in. Endoskeletonis fabricated in stepas described below. When endoskeletonis inserted into base, a top surfaceis exposed as shown, and closed-cell voidsare fully enclosed voids.

In step, a portion of polymeric skinis deposited on exposed surfaceof endoskeleton, as shown in. In the embodiment illustrated in, top surfaceincludes one or more open-celled voids, and therefore a first portion of polymeric skinis deposited within the one or more open-cell voidsand a second portion of polymeric skinis deposited on top surface. As shown, in the embodiment illustrated in, the first portion of polymeric skinand the second portion of polymeric skinare contiguous and form a single continuous polymeric layer. In some embodiments, in step, one or more closed-cell voidsare formed between top surfaceand polymeric skinby selectively depositing the first portion of polymeric skinaround the locations of the one or more closed-cell voids.

In step, end effectorof a computer-aided manufacturing system forms the first portion of polymeric skinthat is deposited within open-cell voidsand the second portion of polymeric skinthat is deposited on exposed surface. The end effectorforms the first portion and the second portion of polymeric skinbased on process parameter values included in an extended NURBS similar to the extended NURBS described in conjunction with. Thus, the CNC commands that cause end effectorto form polymeric skinare generated from end effector trajectories, material flowrate values, and/or other process parameters that are included in the extended NURBS.

In some embodiments, trajectories of a deposition nozzle associated with end effectorare parallel to stress-strain lines determined to exist within polymeric skinwhen multi-material structureis under a specified load. Therefore, reinforcing fibers included in polymeric skinare aligned substantially parallel with such stress-strain lines, thereby increasing the effectiveness of the fiber reinforcement. In such embodiments, the stress-strain lines can be determined via finite-element analysis of a 3D model of multi-material structure, where each element included in such analysis can have a stress tensor direction associated therewith. Thus, the stress tensor direction for a particular portion of polymeric skinthat is associated with an analytical element indicates an ideal deposition nozzle trajectory when material corresponding to that particular portion of polymeric skinis being deposited.

In step, material for baseis removed from fabrication assembly, as shown in. For example, in some embodiments, an NC cutting toolassociated with end effectorcan be employed to remove base. In some embodiments, values for the trajectory and other process parameters of NC cutting toolcan be based on process parameter values included in an extended NURBS similar to the extended NURBS described in conjunction with. Upon removal of base, surfacesof polymeric skinare exposed.

In step, one or more surfacesof polymeric skinare finished or otherwise modified. For example, in some embodiments, a suitable NC cutting tool or other processing instrument (not shown) can be employed to achieve a specified target surface roughness or smoothness of polymeric skin. In some embodiments, values for the trajectory and other process parameters of the NC cutting tool can be based on process parameter values included in an extended NURBS similar to the extended NURBS described in conjunction with.

In step, injection holesare formed in polymeric skinfor the subsequent injection of adhesive, as shown in. In some embodiments, injection holesare microholes drilled via an NC machine. In step, a suitable adhesive is injected into closed-cell voidsand closed-cell voidsvia injection holes, as shown in.

In step, an infiltration process may be employed in some embodiments to further strengthen polymeric skin. In such embodiments, microscopic voids that are known to exist within most polymers are filled with a suitable resin, so that the polymeric material is less brittle. In some embodiments, the infiltration process includes applying a suitable resin on an outer surface of polymeric skinvia a suitable process, for example via a vacuum-bag or pressure-back process. For example, in some embodiments, multi-material structureis wrapped in a plastic bag, vacuum is applied to the interior of the bag so that the bag is drawn against the outer surface of polymeric skin, and a suitable resin is inserted into the bag. Suitable process parameters for such an infiltration process can vary based on multiple factors, including the material(s) included in polymeric skin, the thickness of polymeric skin, the anticipated application of multi-material structure(such as chemical exposure, intensity of impact, etc.), and the like. Examples of process parameters for such an infiltration process can include type of resin, duration of vacuum pressure application, process temperature, and the like. Methodthen proceeds to stepand terminates.

In step, endoskeletonis formed. As described above, endoskeletoncan be formed via any technically feasible manufacturing technique or techniques, such as extrusion, pultrusion, rolling, bending, welding, forging, stamping, and/or the like.

illustrates a CNC processing systemconfigured to implement one or more aspects of the various embodiments. CNC processing systemcan be any computer-controlled workpiece processing system, such as a machining system (mill, lathe, drill, and/or the like), an array of multiple such machining systems, a three-dimensional (3D) printer, a laser-engraving machine, and the like. As such, CNC processing systemis configured to perform one or more precise and repeatable processes on a workpiece, including material addition (e.g., 3D printing), material removal, surface texturization and/or functionalization, and coating application, among others. In the embodiment illustrated in, CNC processing systema table, a CNC positionerand a controller.

Tablesupports workpieceduring processing and, in the embodiment illustrated in, includes a baseand a movable stageon which workpieceis disposed. In some embodiments, movable stageprovides motion of workpiecerelative to positioneralong a single axis. In other embodiments, movable stageprovides motion of workpiecerelative to positioneralong a multiple axes, such as an XY or XYZ stage.

CNC positioneris a multi-axis positioning apparatus, such as a polar axis machine, that locates and orients end effectorin two or three dimensions with respect to workpiece. For example, in embodiments in which end effectorincludes a 3D-printing nozzle, CNC positionersequentially moves the 3D-printing nozzle along specific trajectories over surfaces of workpiece. Thus, in such embodiments, discrete portions of added material can be applied to one or more surfaces of workpiecein a specified order. In other embodiments, CNC positionercan be any technically feasible system for positioning end effector, such as a Cartesian positioner or a hybrid polar and Cartesian positioner.